The invention relates to an apparatus for directly applying a liquid or pasty medium, e.g. a coating medium, onto a moving material web, in particular a web consisting of paper or board. The invention comprises predosing means and final dosing means arranged at a distance from each other and concerns a support for the web as it is being coated.
Coating apparatus are known in which the moving material web to be coated is wrapped around and supported on a selected sector of a cylindrical opposing roll. A predosing means, for example a free jet nozzle application unit or a doctor blade application unit with a pressure chamber, applies the liquid or pasty medium under pressure. A final dosing means provided, for example, with a doctor blade element, finally doses the applied medium. It is disadvantageous in this arrangement if the material web passes through a sharp or small radium curvature between the predosing point and the final dosing point, because large centrifugal forces arise which unpredictably throw parts of the applied coating medium from the material web. Since the coating medium is thrown off relatively irregularly, this often leads to an uneven final coating of the liquid or pasty medium on the material web.
In an apparatus of this type disclosed in DE 43 38 776 A1, the predosing means and the final dosing means are associated with their own respective opposing rolls or their own respective endless belts on which the web rides. The supporting points of the predosing means and the final dosing means can be in such a geometric arrangement that the material web is only exposed to small centrifugal forces in the area of its passage from the predosing means to the final dosing means, and the tension force in the material web can also be regulated by controlled differential speeds of both of the opposing rolls or both of the endless belts. But this construction involves a considerable operative effort and does not permit optimal guidance and support of the material web.